Photomask substrate, photomask substrate forming member, photomask substrate fabricating method, photomask, and exposing method that uses the photomask

Abstract

A photomask substrate with a substantially uniform thickness comprises: a first surface, which is a continuous curved surface whereon a mask pattern is to be formed; and a second surface. The first surface exhibits a square shape that comprises an opposing pair of first set sides and an opposing pair of second set sides and has support parts at end parts along the first set sides. When the photomask substrate is held such that the first surface is in a substantially vertical state, a reference plane that is parallel to a tangential plane of the first surface at the center point of the first surface is defined on the photomask substrate side that is closer to the first surface than to the second surface. At this time, a first distance in the thickness direction between the reference plane and the center point of the first surface is shorter than second distances in the thickness direction between the reference plane and the midpoints of the second set sides.

What is claimed is: 
     
       1. A photomask substrate that consists of a plate shaped member with a substantially uniform thickness, comprising:
 a first surface, which is a continuous curved surface and whereon a mask pattern is to be formed; and 
 a second surface, which opposes the first surface; 
 wherein, the first surface exhibits a square shape that comprises a first pair of opposing sides of the four sides surrounding the first surface and a second pair of opposinq sides of the four sides surrounding the first suface, which extend such that they communicate with the first pair of opposing sides, and a support part, which is for supporting the photomask substrate at its end parts along the first pair of opposing sides; 
 when the photomask substrate is held such that the first surface is in a substantially vertical state, the point at which the axis that passes through the center of gravity of the photomask substrate and extends in the thickness direction of the photomask substrate intersects the first surface is designated as a center point of the first surface; and 
 if a reference plane that is parallel to a tangential plane of the first surface at the center point is defined on the photomask substrate side that is closer to the first surface than to the second surface, then a first distance in the thickness direction between the reference plane and the center point of the first surface is shorter than second distances in the thickness direction between the reference plane and the midpoints of the second pair of opposing sides. 
 
     
     
       2. A photomask substrate according to  claim 1 , wherein when the photomask substrate is held such that the first surface is substantially in the vertical state, the distances in the thickness direction between the reference plane and the portions of the second pair of opposing sides on the first pair of opposing sides are shorter than the second distances. 
     
     
       3. A photomask substrate according to  claim 1 , wherein when the photomask substrate is held such that the first surface is substantially in the vertical state, the distances in the thickness direction between the reference plane and any points along the first pair of opposing sides are substantially the same. 
     
     
       4. A photomask substrate according to  claim 1 , wherein when the photomask substrate is held such that the first surface is substantially in the vertical state, the distances in the thickness direction between the reference plane and midpoints of the first pair of opposing sides are substantially the same as the first distance. 
     
     
       5. A photomask substrate according to  claim 1 , wherein when the photomask substrate is held such that the first surface is substantially in the vertical state, the distances in the thickness direction between the reference plane and the midpoints of the first pair of opposing sides are shorter than the first distance. 
     
     
       6. A photomask substrate according to  claim 1 , wherein when the photomask substrate is held such that the first surface is substantially in the vertical state, the distances in the thickness direction between the reference plane and any points along the second pair of opposing sides are substantially the same. 
     
     
       7. A photomask substrate according to  claim 1 , comprising:
 marks for discriminating the first surface and the second surface. 
 
     
     
       8. A photomask substrate according to  claim 1 , wherein the substrate is made of quartz glass. 
     
     
       9. A photomask fabricated using the photomask substrate according to  claim 1 , wherein a mask pattern is formed on the first surface; and the photomask is supported by an exposure apparatus at the support parts such that the exposure light is projected from the second surface side. 
     
     
       10. An exposing method that exposes a wafer with the mask pattern formed on the photomask according to  claim 9 , comprising the step of:
 performing an exposure in the state wherein the support parts are supported by a photomask support member of the exposure apparatus such that the exposure light is projected from the surface on the side opposite the surface whereon the mask pattern of the photomask is formed, and the surface whereon the mask pattern is formed faces toward the wafer. 
 
     
     
       11. A photomask substrate, wherein a first surface for forming a mask pattern is a rectangle with a diagonal line length of 1,200 mm or greater;
 wherein, the first surface comprises a first pair of opposing sides of the four sides surrounding the first surface and a second pair of opposing sides of the four sides surrounding the first surface, which extend such that they communicate with the first pair of opposing sides, and a first center line, which is a straight line that connects midpoints of the second pair of opposing sides, and a second center line, which is a straight line that connects midpoints of the first pair of opposing sides; 
 the thickness of the photomask substrate is 8 mm or greater; 
 the photomask substrate is held in the state wherein the first surface is substantially vertical; and 
 if a reference plane is defined as a plane that is parallel to a tangential plane at the center point of the first surface and is located at a position that is spaced apart from the first surface on the near side of the first surface, then distances from the midpoints of the second pair of opposing sides to the reference plane are longer by 30-100 μm than a distance from the center point of the first centerline to the reference plane. 
 
     
     
       12. A photomask substrate according to  claim 11 , wherein the distances from any points of the first pair of opposing sides, to the reference plane are substantially the same. 
     
     
       13. A photomask substrate according to  claim 11 , wherein the distances from any points of the second centerline to the reference plane are substantially the same. 
     
     
       14. A photomask substrate according to  claim 11 , wherein the distance from a center point of the second centerline to the reference plane is longer by 150-1500 μm than the distances from the midpoints of the first pair of opposing sides to the reference plane. 
     
     
       15. A photomask substrate according to any one claim of  claim 11  through  claim 14 , wherein a second surface, which opposes the first surface, is substantially parallel to the first surface. 
     
     
       16. A photomask substrate according to any one claim of  claim 11  through  claim 14 , comprising:
 marks for discriminating the first surface and the second surface. 
 
     
     
       17. A photomask substrate according to  claim 11 , wherein the substrate is made of quartz glass. 
     
     
       18. A photomask fabricated using the photomask substrate according to  claim 11 , wherein a mask pattern is formed on the first surface; and support portions, at which the photomask is supported by an exposure apparatus, are in the vicinities of the first pair of opposing sides. 
     
     
       19. An exposing method that performs an exposure using the photomask according to  claim 18 , comprising the step of:
 performing an exposure in the state wherein the support portions are supported by a photomask support member of the exposure apparatus such that the surface whereon the mask pattern of the photomask is formed faces downward.